The Philippine Drug Enforcement Agency says seven Chinese citizens have been arrested in a raid on a clandestine methamphetamine laboratory inside a pig farm north of Manila.

The agency said Thursday that about half a kilogram (one pound) of methamphetamine with a street value of around 2.5 million pesos ($5,400), about 20 kilograms (44 pounds) of the drug ingredient ephedrine, laboratory equipment and various chemicals were confiscated during the raid Wednesday in Pampanga province.

It said charges of illegal drug possession and manufacturing are being prepared against the arrested Chinese, including a woman.

Officials said the drug laboratory in the basement of the hog farm's stockroom may have been built there to mask foul smells from drug production.